Parasites and Pests of Medical Significance in the Maltese Environment - a historical review of culprit species

Parasites or pests with medical significance known to have affected or are affecting the Maltese community are listed. These include several protozoan, helminth and arthropod parasite species. Other arthropod species identified as public health pests in Department of Health publications are also listed. ___________________________________________________________________________________ 1 Institute of Health Care, University of Malta, Gwardamangia, Malta INTRODUCTION The biomedical discipline of parasitology has traditionally been concerned only with the parasitic protozoa, helminths, and arthropods. It is generally assumed that the improvements in the general hygiene that have occurred in the second half of the twentieth century in Malta have made human parasitic infestations a thing of the past. The situation was however very much different prior to the mid-twentieth century and parasitology was an important discipline for the Maltese medical profession. In 1837, it was commented that "taenia and other worms are so frequent, that they are scarcely considered sources of disease" [Montgomery, 1837]. Even today a number of parasitic species still affect Maltese human hosts. METHODS The present study is an attempt to identify the various human parasitic species that have affected the Maltese community throughout the years. The study is based primarily on the 1937-1953 Annual Reports of the Medical and Health Department [M&H, 1937-1953]. Other published sources that deal with aspects of medical parasitology in the Maltese Islands were availed of. More recent parasitic infestations are reported in the Infectious Disease Annual Reports for the period 19911999 [DOH, 1991-2000]. Personal experience of medically important parasitic infestations over a near twenty-year period was also considered. SYSTEMATICS Protozoa ♦ Giardia lamblia This species is usually weakly pathogenic or non-pathogenic to humans. With marked infestation, the large numbers of parasites attached to the bowel wall may cause irritation and low-grade inflammation of the intestinal mucosa, with consequent acute or chronic diarrhoea. Examination of faeces carried out in 1940 revealed one case of Giardiasis cysts [M&H 1937-1953]. The species has been identified in returning tourists particularly from India and Pakistan [personal observation]. Two cases of Giardiasis infection were reported in the 19911999 Infective Disease Reports [DOH, 19912000]. ♦ Trichomonas vaginalis This species restricts itself to the genitourinary system causing marked local symptoms. Sexual intercourse is the usual form of transmission of the infection, but it can also be transmitted by contaminated towels, etc. The species is a common cosmopolitan parasite of both males and females in Malta, though its prevalence may have decreased in recent years [personal observation]. ♦ Leishmania infantum The genus undergoes a complex life-cycle with alternating sexual and asexual reproductive phases involving two host [man or dog, and the sandfly Phlebotomus sp.]. Only the first stage, the nonflagellated amastigote, occurs in the mammalian host. Visceral Lieshmaniasis is the classically described form of the disease in Malta; however in recent years Cutaneous Lieshmaniasis has been described [VellaBriffa, 1985]. The 1991-1999 Infective Disease Reports records 71 cases of Visceral Lieshmaniasis infection and 121 cases of Cutaneous Lieshmaniasis [DOH, 1991-2000]. L. infantum zymodeme MON 1, was found to cause human and canine visceral leishmaniasis. L. infantum MON 78, which has so far been isolated only in Malta, was the agent of human cutaneous leishmaniasis. Both zymodemes were isolated from the same sandfly species Phlebotomus perniciosus [Gradoni, 1991]. ♦ Entamoeba histolytica This species is a parasite commonly found in the large intestine of humans. Invasion of the intestinal mucosal lining results in ulceration causing dysentery. The endemicity of Enteramoeba was only confirmed after the 1913 epidemic. During the period 1941-45, a total of 313 cases were found to be positive on pathological faecal examination [M&H, 1937-53] ♦ Toxoplasma gondii This species is a coccidian protozoan of worldwide distribution that infects a wide range of animals and birds. The normal final host is the domestic cat. Human infections are usually asymptomatic, but can cause severe effects to the fetus when infection occurs during pregnancy. Toxoplasma screening is usually carried out in Malta in cases of recurrent miscarriages and stillbirths. The prevalence rate of toxoplasma antibodies among Maltese pregnant women had been estimated at 23.8%, with an infective incidence of about 2-3 cases per 1000 pregnancies [Portelli, 1995]. ♦ Plasmodium sp. The sporozoan protozoa of this genus are ameboid intracellular parasites of vertebrates, with one habitat in red cells and another in cells of other tissues. Transmission to humans is by the bloodsucking bite of the female mosquito of the genus Anopheles. Reported cases of malaria are generally exogenous cases imported from overseas. During 1991-1999, a total of 17 cases of exogenous malaria were reported [DOH, 19912000]. However a case of endogenous malaria has been reported in the past, while the Anopheles mosquito has been reported to breed in Malta [M&H, 1937-53]. Helminths ♦ Taenia ?saginata ♦ Taenia ?solium. The Tapeworm is a gastrointestinal parasite that has a world-wide distribution and is transmitted to the human host by eating undercooked beef or pork. The Maltese preference of eating well-cooked meat protects against outbreaks of the disease, though uncooked sausages may be a source of infection. Faecal examination in 1940 showed eggs of Taenia in one case [M&H, 1937-1953] ♦ Ascaris lumbricoides The Roundworm is a small intestine parasite of world-wide distribution. It is transmitted by eating viable eggs from contaminated food or soil. The first documented record of an epidemic infestation in Malta occurred during the insurrection of the Maltese against the French rulers at the end of the nineteenth century [Robert, 1804]. The infestation is still occasional encountered in individual patients [personal observation]. ♦ Enterobius vermicularis Pinworm infestation usually occurs by analoral self-contamination and through contamination by food-handlers. It has a world-wide distribution. The infection is the commonest helminthic infestation present today in the Maltese community [personal observation]. ♦ Trichuris tricuria The Whipworm has a world-wide distribution and is transmitted by ingestion of contaminated food. During the period 1940-41 faecal examinations carried out by the Pathology Department revealed two cases showing eggs belonging to this species [M&H, 1937-1953]. Arthropoda Class: Insecta (insects) ♦ Dictyoptera The cockroach species have become particularly adapted to the human environment and have colonised and flourished in artificial pseudotropcal situations. They have become important domestic pests and can be a cause of food poisoning and other enteric infections. Three cockroach species of public health importance have been described from the Maltese Islands [Sultana, 1995].