Infections with a Malaysian dog strain of Ancylostoma ceylanicum in outbred, inbred and immunocompromised mice

The Experimental Use of Syrian Hamsters

The Syrian hamster (Mesocricetus auratus) is a widely used experimental animal model. This chapter focuses primarily on the most current research uses of the hamster. More classical uses are covered only as they pertain to these current uses. Hamsters possess unique anatomical and physiological features, which make them desirable research models. Unlike other commonly used laboratory rodents, hamsters possess a cheek pouch, which can be easily everted and examined at both the gross and microscopic level. The hamster's relative size also allows for better visualization of certain biological systems including the respiratory and reproductive systems when compared to the mouse. Further, laboratory hamsters develop a variety of inherited diseases, which display similarities to human conditions. Hamsters possessing some of these inherited traits are commercially available. They are susceptible to a variety of carcinogens and develop tumors that other research animals less commonly develop. Also they are susceptible to the induction of a variety of metabolic disorders through the use of dietary manipulations. The antagonistic nature of hamsters is used to study the effect of treatment on male aggressive and defensive behaviors. Syrian hamsters display several unique characteristics that make them desired models for carcinogenesis studies.

Host cytokine production, lymphoproliferation, and antibody responses during the course of Ancylostoma ceylanicum infection in the Golden Syrian hamster

The Syrian Golden hamster (Mesocricetus auratus) has been used to model infections with the hookworm Ancylostoma ceylanicum. New molecular immunological reagents to measure cellular immune responses in hamsters were developed and used to determine the impact of A. ceylanicum hookworm infection on host cytokine responses and lymphoproliferation. Initial larval infection with 100 third-stage A. ceylanicum larvae resulted in predominant Th1 responses (upregulation of proinflammatory cytokines) that lasted for the duration of larval migration and continued up to 14 days postinfection (prepatency). Subsequently, development of larvae into egg-laying adult hookworms (patency) coincided with a switch to Th2 predominant responses (interleukin-4 [IL-4]) as well as a marked increase in IL-10 production. This switch also concurred with reduced host lymphoproliferative responses to hookworm antigens. The findings demonstrate a similarity in immune responses between hamsters and humans infected with hookworms, suggesting that hamsters will be a useful animal model species for examining host immunity to human hookworm infections.

Oral transfer of adult Ancylostoma ceylanicum hookworms into permissive and nonpermissive host species

Syrian hamsters become anemic and exhibit delayed growth following oral infection with third-stage Ancylostoma ceylanicum hookworm larvae. Here we describe experiments designed to determine the feasibility of adult worm transfer (AWT) between hosts, a technique that would facilitate the specific study of bloodfeeding hookworms in vivo without prior exposure of the host to larva-specific antigens, permit the ex vivo manipulation of adult parasites prior to reimplantation, and also allow for cross-species transfer of worms. Weanling hamsters given an oral AWT of 40 or 60 mixed-sex A. ceylanicum worms rapidly developed anemia; in the higher-dose group, hemoglobin levels declined from prechallenge levels by 44% within 4 days following AWT. Long-term survival of transferred worms was demonstrated by recovery of parasites from the intestines 42 days after AWT. AWT hamsters acquired humoral immune responses against soluble adult hookworm extracts and excretory-secretory products that were comparable in magnitude to those of animals given a typical infection with larvae. In AWT experiments employing the nonpermissive murine model, C57BL/6 mice given adult worms rapidly became anemic and lost weight in a manner similar to AWT hamsters. Infection of additional mouse strains demonstrated that while C57BL/10 and CD-1 mice also developed anemia following AWT, BALB/c mice were resistant. The technique of AWT to mice may further our understanding of hookworm pathogenesis by allowing the study of adult hookworm infections in a species with well-characterized genetics and an abundance of available reagents.

Ancylostoma ceylanicum in the hamster: observations on the host-parasite relationship during primary infection

The course of primary infection with a hamster-adapted strain of Ancylostoma ceylanicum was studied in inbred DSN and randomly bred WO/GD and WO/CR hamsters. Infective larvae were administered orally and began to develop in the small intestine without embarking on a tissue migration. Only the occasional larva was detected in other organ sites. It was concluded that the developing larvae moulted on days 3-4 and again to the pre-adult stage about 9-11 days post-infection. Worm burdens in infected hamsters were stable for at least 11 weeks after infection. There was no sudden expulsive phase and some adult worms survived for over 200 days. Overall the sex ratio of worms in groups of hamsters killed concurrently was about 50% although occasionally the ratio was biased in favour of one sex in individual animals. The blood packed cell volume (PCV) was significantly depressed 2 weeks following infection and continued to decline until a point of stability was achieved 4-5 weeks post-infection. The PCV subsequently remained depressed throughout the period of observation. Infected hamsters lost weight if kept in groups, but not when housed in separate cages. Groups of animals which lost weight did not recover to normal values within 11 weeks of infection. It is suggested that this model of hookworm infection has scope for exploring aspects of the host-parasite relationship which the canine models cannot fulfill adequately.

Response of dogs to challenge with Ancylostoma ceylanicum during the tenure of a primary hookworm infection

A model of human hookworm infection has been developed which shows that dogs currently infected with small numbers of hookworms are considerably resistant to a challenge infection with a large inoculum of infective larvae. Two groups of dogs were infected with 500 larvae and four weeks after infection one group together with a previously uninfected control group were infected with 5,000 larvae and followed for six weeks. When compared with the secondary infection control dogs, faecal egg excretion and adult worm burdens were reduced by an average of 83 and 78% respectively. Infections had no significant effect on total white cell counts, platelet levels or spontaneous, phytohaemagglutinin- and antigen-induced lymphocyte transformation among the three groups of dogs. Dogs previously uninfected with hookworm developed a marked anaemia when infected with 5,000 larvae but this was not observed in the superinfected group. An eosinophilia developed in all groups and there were no significant differences among the three groups of animals. Specific IgM antibodies developed transiently in all groups of dogs two weeks after infection. IgG antibody levels were significantly greater in the superinfected animals one, two and three weeks after challenge infection compared with the secondary infection control animals; by four weeks there was no significant difference between the two groups of animals. Both groups given the large inoculum of larvae developed specific IgA antibodies one week after the challenge infection and these continued to rise in the superinfected group until termination of the experiment. It is concluded that dogs currently infected with the hookworm, Ancylostoma ceylanicum, demonstrate the development of functional protective immunity.

Resistance of dogs to reinfection with Ancylostoma ceylanicum following anthelmintic therapy

A model of human hookworm infection has been developed which shows that dogs with chronic hookworm infection are considerably resistant to reinfection one month after the termination of the primary infection with anthelmintics. Challenge and control dogs were infected with 1,800 larvae and the infection was followed for six weeks. When compared with control dogs, faecal egg excretion and intestinal adult worm burdens in challenge dogs were reduced by 85% and 77%, respectively. Infection had no significant effect on haemoglobin concentrations, total white cell counts, platelet levels or spontaneous and phytohaemagglutinin-induced lymphocyte transformations in both control and previously infected dogs. Both groups of dogs developed an eosinophilia and lymphocytes responded transiently to stimulation with both larval and adult worm antigens, although there were no significant differences between the two groups of animals. Specific IgM antibodies were transient in both groups of animals following infection. Specific IgG antibodies were present at high levels before infection in challenge dogs when compared with control dogs, and fell transiently after challenge; three weeks after infection, IgG antibodies appeared in the control animals and titres continued to rise during the period of observation. Challenge dogs also developed specific IgA antibodies three weeks after infection, and these remained at high levels, but these antibodies were not detected in control dogs. Thus, dogs infected with this strain of the hookworm, Ancylostoma ceylanicum, which has been shown to infect man, develop functional protective immunity. These findings improve prospects for vaccine development.

Scanning electron microscopy of Ancylostoma ceylanicum and its site of attachment to the small intestinal mucosa of the dog

The relationship between the hookworm Ancylostoma ceylanicum and the host intestinal mucosa in situ has been examined by using an in vivo fixation technique and scanning electron microscopy. Heads of the adult worms were buried deeply in the mucosa of the dog's small bowel. At some sites of attachment there was severe atrophy and ulceration of the immediately surrounding villi. Superficial deposits of fibrillar material with many enmeshed erythrocytes were associated with these attachment sites. When adult worms became removed after fixation, large numbers of erythrocytes could be seen at the base of the ulcers. Examination of the morphological details of adult A. ceylanicum revealed the characteristic mouthparts of large outer ventral teeth and smaller inner teeth. The distance between adjacent transverse cuticular striations was measured as 5.2 microns. The wide separation of the externolateral ray from the closely related mediolateral and posterolateral rays was illustrated together with the functi characteristic mouthparts of large outer ventral teeth and smaller inner teeth. The distance between adjacent transverse cuticular striations was measured as 5.2 microns. The wide separation of the externolateral ray from the closely related mediolateral and posterolateral rays was illustrated together with the functi characteristic mouthparts of large outer ventral teeth and smaller inner teeth. The distance between adjacent transverse cuticular striations was measured as 5.2 microns. The wide separation of the externolateral ray from the closely related mediolateral and posterolateral rays was illustrated together with the functional relationship of male and female copulating worms.

Transmission electron microscopical studies of the site of attachment of Ancylostoma ceylanicum to the small bowel mucosa of the dog

The host-parasite interaction at the site of attachment of the adult hookworm, Ancylostoma ceylanicum, to the small bowel mucosa of the dog has been examined by transmission electron microscopy. The lamina propria around the heads of the worms showed intense infiltration with neutrophilic and eosinophilic leucocytes, and plasma cells were also prominent. Erythrocytes were extravasated within the lamina propria while the portions of mucosa engulfed into the buccal cavities of the worms were necrotic and included aggregates of collagen fibres. Within the lumina of the worms were erythrocytes in varying stages of lysis together with other necrotic debris. The mucous membrane adjacent to the heads of the worms was ulcerated while more distant enterocytes were small, distorted and displayed various degrees of microvillar loss. Many mucosal blood vessels had platelet aggregates within their lumina but no fibrin deposition was observed. Vessels were often seen in the bases of the ulcers and were prone to rupture. Erythrocytes and leucocytes were seen in the dog intestinal lumen in close proximity to the bodies of the worms.